With the development of the display technology, organic light emitting diode (OLED) displays have become one of the focuses in the field of the current flat panel display, and more and more organic light emitting diode display panels enter the market. Compared with the traditional thin film transistor liquid crystal display (TFT LCD) panels, the OLED display panels have faster response, higher contrast and wider angle of view.
The traditional organic light emitting diode panels are driven to emit light by means of currents generated by driving transistors (thin film transistor, TFT) in a saturated state. However, upon inputting of the same gray scale voltage, transistors of different threshold voltages generate different driving currents, which causes inconsistency in the driving currents, so that the brightness uniformity among pixels is poor. Therefore, the method of employing a pixel compensation circuit which comprises a compensation circuit and a driving circuit within a pixel is generally adopted to resolve the problem of poor brightness uniformity, namely the influence of the threshold voltage Vth of a driving TFT is eliminated through the pixel compensation circuit. However, the pixel compensation circuit disposed in each pixel leads to increasing the number of the TFT, decreasing the aperture ratio of the pixel and increasing the costs, so that given the condition of the same pixel driving current, the current density of an organic light emitting layer increases, which easily leads to the aging of the material of the light emitting layer and declines the service life of the whole OLED panel.
Therefore, how to improve the aperture ratio of a pixel unit due to occupation by a pixel circuit is a technical problem to be solved for those skilled in the field.